There is a definite need for a mechanical circle-cutter today, particularly in view of the advent of plasma cutters and the need for efficiency in making such cuts, as in the commercial manufacture of metal discs. The conventional method in prevalent use today is to utilize a template to aid in inscribing the desired circle upon the workpiece which is frequently of sheet steel. Making a template involves a considerable waste of time.
Another method is to establish a pivot point on the workpiece and then inscribe circle with the pivot point as the center. The use of marking the pivot point mars the surface, making the end-product less desirable, sometimes to such an extent as to require remedial welding to obviate the scar.
One additional way of making a circular cut has been to utilize a magnet as a pivot point. This procedure, however, has a distinct disadvantage in that the magnet often covers the workpiece area to be cut, which limits the size of the circle which can be cut.
The closest prior art with which I am familiar is U.S. Pat. No. 2,483,229 issued to Parker in 1949, which we developed in a patentability search. For some unknown reason, to the best of my knowledge, this circle-cutting machine is not available on the market. It would appear that, since the weight of the entire cutting structure is off-set relative to the support arm 12, the key 18 and keyway 15 will quickly wear and, as a consequence, cause the nozzle 36 of the torch to be oriented off-vertical and introduce error into the cutting operation. The keyways will fill readily with grit, requiring frequent cleaning and introducing error in the cuts.
It will also be noted that the support arm is not capable of free swinging movement since the sleeve 5 has been positioned to lock the device at a predetermined elevation, for operation of the cutter. There is a limit as to how close an operator can cut a hole, to the edge of the workpiece. In addition, material to be cut must have at least a minimum of thickness in order to be able to support the Parker cutter. Also, it is impossible to adjust the height of the cutting torch without losing your center because it requires rotation of arm 12 and shaft 3.
In addition to the above, the bushing in the pivot point will wear rapidly since grit will enter same, requiring substantial maintenance and cleaning. No ready means is provided for setting the torch so as to produce a circle having a predetermined radius. Having the main frame off-center, as in the Parker patent, makes it difficult to measure from the edge of the material to the center of the circle and causes parts to wear excessively, the torch to tip, and cut to be made at an angle. No provision is made to adjust in small increments the radius of the circle to be cut. No provision is made for supporting the handle of the torch or plasma lines or for attaching automatic turning apparatus for making the cut. Also, there is a limit as to how far the circle to be cut can be disposed from the edge of the workpiece.
U.S. Pat. No. 2,523,237 issued to Richardson shows a torch cutting tool which utilizes a punched center hole and a scribed line along which the workpiece is to be cut. A wheeled carriage 11,52 moves about the center-points 16,54 to guide the torch along the desired line.
U.S. Pat. No. 2,603,475 issued to Rotsch also utilizes a carriage which rides upon the workpiece and supports the cutting torch as it is carried around the pivot point 90.
U.S. Pat. No. 2,886,305 issued to Strahan also uses a carriage 20 which carries the torch 16 as it rides over the surface to be cut.
U.S. Pat. No. 3,547,424 issued to Brown shows a template guided circle-cutting attachment driven by gear boxes and a motor.
U.S. Pat. No. 4,021,025 issued to Frame discloses a circle-cutter which utilizes a circular platform which is attached to the plate to be cut and a cutting torch carried by, and adjustable relative to, the rotatable platform and being movable in a circular path therewith.
U.S. Pat. No. 4,173,333 issued to Wise discloses a torch guide for cutting a beveled edge, incapable of cutting a circle.
U.S. Pat. No. 4,411,410 issued to Sumner discloses a complicated apparatus for cutting openings in pipes, which use a locator 82 about which the torch 96 is rotated in response to pipe contour tracking means.
None of the above patents are constructed and operate in the manner disclosed and claimed herein.